1. Field of the Invention
The present invention relates to a solar cell module and a production process thereof.
2. Related Background Art
Solar cells which utilize solar energy are expected to be a clean and reproducible energy source, from residential use to large scale electricity generation.
In particular, the use of solar cell modules on roofs of buildings is predicted as a means of utilizing limited spaces. Solar cell modules built in roof structures hold big promise to reduce the construction cost of buildings because such solar cell modules are installed as part of the construction process and do not need frames for installation.
Durability against environmental conditions such as temperature, humidity, and mechanical shock are required when solar cells are used. For this purpose, solar cell modules used conventionally are made by sealing the solar cell elements in a filler and by covering the surface with a durable plastic film or glass plate.
A most preferable structure for integral type solar cell modules built into a building roof requires that the solar modules be made in the following manner: the front side surface is sealed by a durable plastic film protector; a reinforcing plate is used at the back side surface without using a frame; and the non-generating area is applied to plasticity processing integrally with the reinforcing plate.
A solar module of such structure, which is mechanically reinforced by folds formed therein, not by use of a frame, has the following advantages:
It has no joint between the main body of the cell elements and the frame, and has no need for water proof treatment; thus it is advantageous for water flow thereover. It also does not need material and operational steps for providing the frame, and results in a cost reduction of the installation. It is also lighter than the framed module, and is easy to handle.
Stiffness of the module can be advantageous for joining and overlapping at the construction step; consequently a strong and reliable construction can be made.
When a usual metallic material is used for the back reinforcing plate, it can be set on the building roof just like the usual roofing material. Consequently, reliability of the module as the roofing material can be increased; thereby, popularization of the module can be assured with the interchange ability of the module with the usual roofing material.
The present inventors have developed a solar cell module that includes a solar cell element, a back reinforcing plate, and a durable plastic film for environmental protection.
The protection of the back reinforcing plate by a durable plastic film is required to prevent peeling between the cell elements and the back reinforcing plate, and to protect from the leakage of water from rain.
There were observed the following problems in such a solar cell module, which is composed of solar cell elements and a back reinforcing metal plate and with integrally applied plastic processing.
At first, the filler within the module tends to be cracked at the folded portions, the filler being used to protect the cell elements and because the folding work creates large stresses in the folded portion peripheral of the filler material. This cracking causes problems not only to the appearance of the module but also deterioration of the cell elements due to the leakage of water through the cracked channel reaching to the cell elements. There is also the problem that the protection film tends to crack.
Usually a filler holder is embedded in the filler material of the solar cell module, and the peeling occurs between the filler material and the holder; the holder is torn because of the bending strain and the folded portion is subjected to whitening. This whitening also gives rise of problems not only in the appearance of the module but also deterioration of the elements caused by the flow of water. The filler holding material is embedded to protect the solar cell elements, it also prevents hot filler leakage during the laminating step of the solar cell modules under heat and vacuum, and it also guides the air to the outside of the module during the defoaming under heat and vacuum.
For these problems, the present inventors proposed, in JP-A 7-131048, a method in which the holder is removed from the folded portion. However, even this means is not satisfactory for producing solar cell modules commercially because of the following problems.
Elastic material that can absorb mechanical shock is used for the filler to protect the solar cell element. The filler tends to return to the original flat plate shape after the solar cell module is shaped by folding, since the filler cannot be folded because of the elasticity restoration, even after the back reinforcing plate is folded. There is a problem of so-called "spring back", as a result of which the required folding cannot be obtained and an insufficiently sharp angle results. There is also a problem in which the peripheries of the module tend to deform wavelike. These problems occur when a low strength backing plate for reinforcement, for example a thin steel plate, is used.
Referring to FIG. 19, the peeling problem is explained. Peelings occur at the location shown by reference numeral 1905 when solar cell module 1901 is folded towards the side of back reinforcing plate 1902 and the force of elasticity restoration, which is the force of filler 1903 tending to return to the original shape before the folding, exceeds the adhesive strength between filler 1903 and back reinforcing plate 1902.
This peeling problem may occur during the folding, and it also may occur after a long period of outdoor exposure even though there was no problem immediately after the folding. In the case where peeling occurs only in a limited part, the space between the filler and the back reinforcing plate forms a channel for water flow and the electricity generation ability of the solar cell elements deteriorates.
There is also a problem that the presence of thick filler material causes difficulty in the folding of various and complicated bending shapes of the solar cell module.
The bending has problems also for workability.
When a so-called "bender", the most simple bending machine that bends material placed between a blade and a mold, is used, it is necessary to lift the blade up and down for every bending operation; it is time consuming and makes cost reduction difficult. This problem is more severe for solar cell modules that have many folded parts. When the module has an elongated dimension along the folding side, it is necessary to use a blade and a mold that are longer than the dimension, and the necessary large power makes the bending difficult.
There is also a problem when a molder usually called a "roll molder" is used to fold the solar cell elements for the purpose of avoiding the problem associated with the use of the bender.
By referring to FIGS. 20-22, roll molders are explained.
The modules are molded step-by-step in several stages between the upper and lower molding rollers. Various shapes of the rollers are used for the roller molding.
FIG. 20 shows a schematic front view of upper and lower molding rollers.
The module material to be molded 2001 is placed between the upper roller 2002 and lower roller 2003, as shown in FIG. 20, and molded. The rollers have the function of transporting the module material 2001 at a constant speed in addition to the function of bending. The rollers also have the function of making necessary adjustments.
FIG. 21 is a schematic drawing of a group of the upper and lower rollers.
The module material is transported from the right side to the left side of the figure, and molded gradually. Complex and good molding is possible when the number of rollers is larger, since the molding step can be divided into many stages.
FIG. 22 explains the molding process in the roller molding.
The material is processed gradually in many steps as shown in FIG. 22 and molded to the final shape.
The merits of this molding method are that the complex cutting face of the mold can be made in one series of processing, it is possible to make a folding mold having the long shape of the solar cell module, and it is also possible to mold materials in good surface condition, with good shape and size precision.
However, there is a problem in this method in that cutting and concavities may be formed in the filler when the solar cell module is processed. There is also another problem that the process may cause scarring and cutting of the weather resistant plastic film.
These problems are explained by referring to FIG. 23. FIG. 23 is a schematic front view of the upper and lower rollers and a solar cell module that is in the course of molding. As shown in the figure, the face of the solar cell module 2301 is pressed at the two points 2307, by upper molding roller 2305, when the solar cell module 2301 is folded towards the side of back reinforcing plate 2302. Since the filler is thick and has large elasticity in this part, problems of depression and tearing of the filler occur. Also, the problems of scarring and tearing of the wear resistant plastic film occur at the roller edges. In addition, it is a problem that molding size precision is impaired by the absorption of the molding load by the thick filler.
These are not only problems in the appearance of the finished module, but there also are the problems of cracking and peeling of the filler by concavities and cuts in the filler; the scars or damage to the filler may deteriorate the performance of the solar cell module by water penetration along the peeling and damage of the weather resistant film. It is necessary to increase the roller pressure in order to get sufficient folding effect of the rollers, because the pressure tends to be absorbed by the filler; and the high pressure also deteriorates the performance of the solar cell element.
As described above, the conventional method of shaping a solar cell module by folding is difficult and unreliable; thereby, deterioration of the solar cell modules has occurred in long term service.